Motor-driven type power assisted steering control apparatus

Abstract

A motor-driven type power assisted steering control apparatus has a torque sensor which is provided with first and second displacement-electric signal converting units and a control unit which is adapted to break a motor current and to interrupt application of a voltage to an electromagnetic clutch as soon as abnormality in the torque sensor is detected on the basis of the electric signals of the first and second displacement-electric signal converting units.

We claim: 
     
       1. A motor-driven type power assisted steering control apparatus in a steering system having a rack which comprises: a speed sensor for detecting car speed;   a torque sensor comprising torque-displacement converting means disposed on a steering shaft for converting a torque of steering into an amount of displacement of said torque-displacement converting means, at least one displacement conveying means for mechanically transmitting the amount of displacement of said torque-displacement converting means, and first and second displacement-electric signal converting means for converting the amount of displacement given by said displacement conveying means into electric signals;   a d.c. motor;   an electromagnetic clutch directly connected to the output shaft of said d.c. motor and operatively connected to said rack; and   control unit having means for receiving electric output signals from said speed sensor and said first and second displacement-electric signal converting means, means for judging whether a difference in value between the electric output signals from said first and second displacement-electric signal converting means is higher than a predetermined signal value, and means for deenergizing said d.c. motor and said electromagnetic clutch based on the judgment that said torque sensor is abnormal, when said difference in value is higher than said predetermined value, whereby an auxiliary torque of said d.c. motor is disconnected from said steering shaft.   
     
     
       2. The motor-driven type power assisted steering control apparatus according to claim 1, wherein said torque sensor comprises first and second ones of said displacement conveying means which respectively convey a mechanical force from said torque-displacement converting means to said first and second displacement-electric signal converting means. 
     
     
       3. The motor-driven type power assisted steering control apparatus according to claim 1, wherein said control unit comprises first and second steering torque measuring means which receive electric signals from said first and second displacement-electric signal converting means to compare the values of the electric signals, and a torque-sensor-abnormality judging means for determining abnormality in said torque sensor based on a value obtained by subtraction of the values of said electric signals. 
     
     
       4. The motor-driven type power assisted steering control apparatus according to claim 1, wherein said control unit is provided with a motor current determining means and a motor current memorizing means, in which said motor current determining means comprises means for determining a desirable motor current on the basis of steering torque and car speed from among motor currents stored in said motor current memorizing means, and for rendering the motor current to be zero when an abnormality is detected in said torque sensor. 
     
     
       5. The motor-driven type power assisted steering control apparatus according to claim 4, wherein said control unit is provided with a motor current control means electrically connected to said d.c. motor to control a current to said d.c. motor on the basis of an output from said motor current determining means.